The significance of immunologic mechanisms is being evaluated in primary open-angle glaucoma. We used light and electron microscopy to demonstrate the presence of type IV collagen, fibronectin, and noncollagenous protein in the human trabecular meshwork using immunofluorescence and immunoperoxidase. Factor VIII antigen, a marker for vascular endothelium, was demonstrated in the conjunctival blood vessels of controls, but was absent in Schlemm's canal and the trabecular meshwork of both glaucomatous and nonglaucomatous eyes. We did not detect immunoglubulins IgG, IgM and IgA or C3 component of complement.